PROJECT SUMMARY ABSTRACT Pregnancy loss occurs in ~20% of women with a clinically recognized pregnancy. Couples with histories of pregnancy loss represent a large portion of those trying to conceive, but treatment is limited to widely inaccessible fertility services. Data from the Effects of Aspirin in Gestation and Reproduction (EAGeR) Trial has shown that preconception low-dose Aspirin therapy increases birth rates in women with histories of pregnancy loss when preconception chronic low-grade inflammation, determined by C-reactive protein, is present. There is a critical need to understand pathways that result in preconception chronic low-grade inflammation. This would help to identify a broader group of women whom would benefit from aspirin therapy and inform the use of aspirin in reproductive medicine. We hypothesize that prior exposure to common sexually transmitted infections (STIs) can lead to long-term immune dysregulation and defective tissue repair. Among women with histories of pregnancy loss, STI serology may indicate subsequent risk of adverse events or represent a group of women who would benefit from preconception anti-inflammatory therapy. Prevalent and mostly asymptomatic STIs such as Chlamydia trachomatis and Mycoplasma genitalium can ascend to the upper genital tract causing endometrial inflammation, tissue damage and scarring. Unfortunately, most women acquire these STIs as young adults, but do not know they were ever infected. The concept of ?trained innate immunity? posits that innate immune cells can develop a long-term proinflammatory phenotype following infectious stimuli induced through epigenetic changes to immune and epithelial cells. Indeed, these STIs are linked to tubal infertility but associations with other measures of impaired fecundity are limited. The specific aims of this proposal will: 1) determine if seropositivity to Chlamydia trachomatis and Mycoplasma genitalium influences time-to-pregnancy, pregnancy loss and birth rates in women with histories of pregnancy loss while adjusting for other STIs known to infect the upper genital tract. 2) Determine if STI seropositive women have a unique blood immune and angiogenic profile compared to seronegative women. 3) Determine if STI seropositive women previously randomized to Aspirin therapy as part of the EAGeR trial (results described above) have improved birth outcomes. This study will include 1078 women from the EAGeR trial. All women have histories of pregnancy loss but no history of infertility. Access to preconception data from a study with extremely detailed reproductive outcomes is unique. Additionally, our team includes a world-leader in STI diagnostics, which allows for robust serological measurements. We will also leverage the expertise of our team members, currently funded to develop methods to address generalizability, to transport our results to our target population of US women with histories of pregnancy loss using the National Survey of Family Growth. Given the profound increase in STI prevalence in the U.S. and the frequency of pregnancy loss, this study and our future work could impact a large number of women.